This invention relates to monolithic ceramic capacitors having a pair of main electrodes extending to opposite ends of a very small capacitor body, and more particularly to such capacitors having at least two auxiliary electrodes between the main electrodes.
Monolithic ceramic capacitors consist of a dielectric ceramic body typically having two groups of main electrodes buried therein. One electrodes-group extends to a separate side other than the other group to permit termination and provide electrical access. The electrical capacity so obtained is a function of many variables. Major variables are dielectric thickness between adjacent electrodes, dielectric constant K of the ceramic, and registration between adjacent electrodes. It is not unusual for capacity values of a production lot to vary 40%.
Misregistration between adjacent electrodes can be eliminated as a source of variation in capacitance by designing the electrode patterns so that there is a constant predetermined area of overlap between adjacent electrodes as is described in my patent, U.S. Pat. No. 3,896,354 issued July 22, 1975 that is assigned to the same assignee as is the present invention.
Also, when tighter capacitance tolerances are desired than obtainable in a given process, it is known to abrade a cavity in the body, removing central portions of some of the electrodes and surrounding ceramic to reduce the capacity to the desired value. Such a technique is described by W. Hatch in U.S. Pat. No. 3,456,170 issued July 15, 1969 and assigned to the same assignee as is the present invention. However, the abrading technique is not practical for use with very small capacitors wherein the electrodes overlap area is small compared to that of the capacitor body profile.
Another technique for adjusting capacity includes providing several auxiliary electrodes that extend to yet another surface of the ceramic body. These auxiliary electrodes are buried between two main electrodes that extend to the same main terminal of the capacitor and, when connected externally to the other main terminal of the capacitor, the capacitance increases.
It is an object of this invention to provide an alternative method for adjusting the capacitance value of a monolithic ceramic capacitor.
It is a further object to provide an improved adjustable monolithic ceramic capacitor applicable to capacitors of very small size.